JPH06148001A - Optical fiber composite power cable - Google Patents

Abstract

PURPOSE:To enable early and positive detection of ground fault of cable by laying an optical coated fiber in the longitudinal direction of shielding layer of a power cable while winding on the outer periphery of an insulator at a pitch specific times as long as the outer diameter of the shielding layer. CONSTITUTION:Multiple copper strands are wound spirally on the outer periphery of an outer semiconductor layer 5 composing a power cable 1 thus providing a shielding layer 8 and a housing 9 of plastic, for example, is applied thereto. About four(one or more) optical coated fibers 7 are laid in the longitudinal direction at a part of the shielding layer 8. The fibers 7 are wound spirally at a pitch of 2.5-20 times of the outer diameter of the shielding layer 8. The coated fibers 7 are connected with a distributed temperature measuring system and pulse light is transmitted thereon in order to measure variation of the intensity of Raman scattering light with time. This constitution allows continuous measurement of temperature distribution in the longitudinal direction of cable thus allowing detection of temperature rise at the time of ground fault of the cable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber composite power cable in which optical fibers for measuring the temperature distribution of the cable are combined.

[0002]

2. Description of the Related Art In recent years, overhead cables in urban areas
From the point of view of transportation and aesthetics, the undergrounding is progressing regardless of the power cable and the communication cable. In particular, overhead power cables may hinder fire-fighting activities in the building area, and there is a strong demand for undergrounding. For this reason, the undergrounding of power cables in recent major cities has been significantly progressing. However, if the power cable is underground, it takes a lot of time to recover from the accident if a cable accident occurs.Therefore, it is necessary to monitor the power cable and detect abnormalities early to prevent damage to other cables. The need for measures is increasing. It is also important to locate the cable failure point after the accident in a short time.

Further, in general, power cables are often designed and laid with a margin for current capacity, and in response to the recent rapid increase in power demand, the allowable temperature is monitored while monitoring the temperature of the actual cable operating state. It is important to manage the current that can be transmitted below. From the above background, it seems that the optical fiber composite power cable in which the optical fiber cable having the temperature distribution detection function is combined with the power cable is used to manage the allowable current of the power cable and to search for the cable abnormal point. It has become.

OTDR (Optical Time Domain) is used for temperature distribution measurement using this optical fiber.
The Reflectometry method is used,
The principle of the temperature distribution measurement will be described with reference to the Raman scattering diagram of FIG.

Letting ωo be the frequency of the light pulse incident on the optical fiber, ωf (ωf = ΔE) is the frequency of the light corresponding to the difference ΔE between the ground level and the excitation level of the energy level of the fiber constituent material (eg SiO ₂ ). / H, h; Planck's constant). When a strong optical pulse is incident on the optical fiber, energy is exchanged between the incident photon and the optical fiber constituent material, and is mixed with the Rayleigh scattered light having the same frequency as the incident light (ωo), which is called Raman scattered light. Higher frequency (ωo + ωf) and lower frequency (ωo−) than the incident light
The light of ωf) is observed.

This is because the photon (ω
o) is absorbed by the fiber constituent material in the ground state, and when the photon is emitted, the material becomes Stokes light (ωo−ω) when it is in an excited state having a higher energy level than the original ground state.
f) is emitted and vice versa.
+ Ωf) is emitted.

The frequency deviation ωf of the Raman scattered light is a value peculiar to the substance and is proportional to the difference ΔE of the thermal energy levels, and is about 13 T (1
0 ¹² ) Hz.

The intensity of the Stokes light and the anti-Stokes light has temperature dependence shown in FIG. 7, and the temperature dependence of the anti-Stokes light is relatively large. The distributed optical fiber temperature sensor observes the change over time in the intensity ratio of the Stokes light and anti-Stokes light of the backward Raman scattered light that is scattered in this optical fiber and propagates in the direction opposite to the traveling direction of the incident light. The temperature ratio in the longitudinal direction of the cable is measured by converting the intensity ratio of 1 to the temperature and converting the time from the incidence of the pulsed light to the reception of the reflected light into the distance from the incident point to the reflection point.

Next, the structure of the temperature measuring system will be described. FIG. 5 is a block diagram of a distributed temperature measurement system using an optical fiber. The measurement system is roughly divided into an optical fiber core wire 7, a measurement unit 20, a digital averaging unit 29, and a computer 30 including a display unit.
Consists of.

The optical fiber core wire has a function of detecting the temperature according to the above-mentioned principle and a function as a transmission path of the temperature detection information. The measurement unit 20 includes an optical unit 21 and a photoelectric conversion unit 24, and the optical unit 21 receives a trigger signal from the digital averaging unit 29 and causes a pulse light source 22 (for example, a laser diode) of monochromatic light to emit light, Through the spectroscopic device 23, the optical fiber core wire 7
Incident on. Further, the optical unit 21 separates the reflected light from the optical fiber core wire 7 into Stokes light and anti-Stokes light by the spectroscopic device 23. The photoelectric conversion unit 24 converts the separated Stokes light and anti-Stokes light into electric signals by the light receiving elements 25 and 26 (eg, silicon avalanche photodiode; Si-APD), and
The signals are amplified by the amplifiers 27 and 28 and sent to the digital averaging unit 29.

The digital averaging unit 29 performs the above measurement a large number of times (for example, 10 ⁹ times) at high speed, converts this measurement signal into a digital signal, and removes noise by averaging processing. The computer 30 controls the entire measurement, and the digital averaging unit 2
It downloads data from 9, converts it into temperature and distance, and displays it on a display screen or prints it out.

From the pulse light source 22 to the optical fiber core wire 7
The time t until the pulsed light incident on the photodetector reaches the light receiving elements 25 and 26 is t = 2Lo / v (where Lo is the optical fiber core wire from the incident end of the pulsed light to the point where backscattering occurs). 7 and v is the speed of light in the optical fiber.) Therefore, after the digital averaging unit 29 triggers the pulse light source 22 to emit pulsed light, the light receiving elements 25 and 26 are By measuring the time t until the detection signal is output, the position where the backscattered light is generated can be located, and as a result, the position where the temperature abnormality of the power cable 1 has occurred can be obtained.

The optical fiber distributed temperature measuring system described above has already been commercialized and is sold by the applicant as "optical fiber distributed temperature sensor DFS-1000". An example of the measurement performance of this system is shown below. Temperature measurement accuracy ± 1 ° C. Temperature measurement range -20 to + 150 ° C. Measurable distance 2 km Distance resolution 1 m Measurement time required about 10 seconds In addition, FIG. 8 shows an example of Raman backscattering measurement of the system, and FIG. 9 shows the measurement of FIG. The example which converted the data of an example into temperature is shown.

Furthermore, a patent application has already been filed by the applicant of the present invention for an optical fiber composite power cable which is a composite of an optical fiber and an electric power cable adapted to the above-mentioned optical fiber distributed temperature measuring system (Japanese Patent Application No. Sho 63). -28669
8 and Japanese Patent Application No. 63-296101; "Power cable and its temperature distribution measuring method").

[0015]

However, such a conventional technique is satisfactory as a temperature distribution measurement for the purpose of controlling the allowable current of the cable.
It has sufficient detection capability for local temperature rise (hot spot) that occurs in a relatively short section of the cable such as a cable ground fault, and that occurs in a non-rotationally symmetrical manner about the cable axis. There was a problem that not.
In view of the above points, an object of the present invention is to provide an optical fiber composite power cable that can detect a ground fault accident early and reliably.

[0016]

The optical fiber composite power cable of the present invention comprises a cable center conductor insulated with an insulator,
In a power cable in which a shield layer including an outer conductor is provided on the outer circumference of the insulator, and an outer jacket is provided on the outer circumference of the shield layer, an optical fiber core wire is provided on a part of the shield layer along the longitudinal direction thereof. , The optical fiber core wire is 2.5 to the outside diameter of the shielding layer.
The problem is solved by winding around the outer circumference of the insulator at a pitch of 20 times and detecting an accident of the power cable based on the Raman scattered light intensity of the optical fiber core wire.

Further, according to the present invention, in a power cable in which a cable center conductor is insulated with an insulator and an outer jacket is provided on the outer periphery of the insulator, an optical fiber is provided in a part of the outer jacket along the longitudinal direction thereof. A core wire is provided, and the optical fiber core wire is wound around the outer circumference of the insulator at a pitch of 2.5 to 20 times the outer diameter of the insulator, and an accident of a power cable is detected based on the Raman scattered light intensity of the optical fiber core wire. It can be detected.

[0018]

The present inventor has developed a method for simulating a ground fault of an electric power cable as shown in FIG. 10 as a clue for solving the above-mentioned problems (1992 Proceedings of the Japan Society of Electrical Engineers Proceedings 1444 " Development of cable failure point evaluation method by temperature detection ", Amano et al.). This method creates a test power cable in which a defect (0.1 mmφ conductor) is embedded in the insulator during the power cable manufacturing process, applies a high voltage to this test power cable, and powers it at the time of a ground fault. The temperature distribution of the cable is measured. With this temperature distribution measurement, if the optical fiber core wire is wound around the insulator at a pitch of 2.5 to 20 times the outer diameter of the shielding layer or the insulator, it is possible to obtain precise voltage according to various voltage classes and various nominal cross-sectional areas. It was discovered that the cable temperature distribution can be measured.

In the present invention, the optical fiber core wire provided on the shield layer or the jacket of the power cable is wound around the outer periphery of the insulator at a pitch of 2.5 to 20 times the outer diameter of the shield layer or the insulator to form an optical fiber. By measuring the time change of the intensity ratio of the Stokes light to the anti-Stokes light of the backward Raman scattered light when pulsed light is incident, a local temperature rise asymmetric with respect to the cable center axis in a short section of the cable is detected. And at the same time as discovering the ground fault of the power cable early,
It is possible to calculate the distance from the cable terminal to the accident occurrence point and locate the accident occurrence point.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view of an optical fiber composite power cable according to the first embodiment of the present invention. As shown in the figure, the optical fiber composite power cable 1 has an inner semiconductive layer 3 and a crosslinked polyethylene insulation layer (insulator) on the outer periphery of a cable center conductor 2 in which a plurality of copper strands are twisted to form each divided conductor.
4, the outer semiconducting layer 5 is sequentially provided, and the inner semiconducting layer 3, the polyethylene insulating layer 4 and the outer semiconducting layer 5 are usually formed by a coextrusion method so that the space between the inner semiconducting layer 3 and the polyethylene insulating layer 4 is increased. , And the cross-linked polyethylene insulating layer 4 and the outer semiconductive layer 5 are integrated.

A shield layer 8 is provided on the outer periphery of the outer semiconductive layer 5 by spirally winding a large number of copper wires, and a cable sheath (cover) 9 made of plastic, metal or the like is coated on the shield layer 8. ing.

Further, a part of the shielding layer 8 is provided with four optical fiber core wires 7 in the circumferential direction along the longitudinal direction thereof, and the optical fiber core wires 7 are provided as shown in FIG. The element wire 7a is covered with a metal layer 7c of copper, aluminum, stainless steel or the like, and the gap between the metal layer 7c and the optical fiber element wire 7a is powder lubricated with ceramic powder such as alumina (Al ₂ O ₃ ) or talc powder. The agent 7b is enclosed.

In the first embodiment, the optical fiber core wire 7 is used.
Although four are provided on the outer periphery of the insulating layer 4, the present invention is not limited to this, and at least one or more may be provided.

FIG. 1 is a partially exploded view showing the spirally wound shape of the shielding layer 8 with the cable sheath 9 of the optical fiber composite power cable 1 of the first embodiment removed. The pitch of the spiral winding of the optical fiber core wire 7 which is a part of the shielding layer 8 is set to 8 times the outer diameter of the shielding layer 8 in the present embodiment, but the pitch is not limited to this.

As described above, the optical fiber combined with the power cable is connected to the distributed temperature measuring system of FIG. 5 described in the prior art, and pulsed light is incident on the optical fiber to control the intensity of Raman scattered light. By measuring the time change, it is possible to measure the continuous temperature distribution in the cable longitudinal direction, and it is possible to detect the temperature rise in the cable ground fault.

Next, FIG. 4 shows a sectional view of an optical fiber composite power cable 1A according to a second embodiment of the present invention, and the same parts as those in the first embodiment will be designated by the same reference numerals.
In the second embodiment, the insulating layer 4 of the power cable 1 shown in FIG.
The optical fiber core wire 7 shown in FIG. 3 is provided on the outer periphery of the optical fiber core wire, and the optical fiber core wire 7 is spirally wound around the outer periphery of the insulating layer 4.
An outer jacket 9 is provided on the outer circumference of the optical fiber composite power cable 1A. The winding pitch of the optical fiber core wire 7 may be any value between 2.5 and 20 times the outer diameter of the insulating layer 4. This optical fiber composite power cable 1A
Similarly to the first embodiment, by connecting to the distributed temperature measuring system of FIG. 5, a continuous temperature distribution in the cable longitudinal direction can be measured, and a temperature rise due to a cable ground fault can be detected. Although the preferred embodiment has been described above, this does not limit the scope of the invention. The scope of the invention should be limited only by the claims which follow. Many modifications within the spirit and scope of the invention will be apparent to those skilled in the art from the above description.

[0027]

As described above, in the present invention, the optical fiber core wire of the optical fiber composite power cable is
Stokes of backward Raman scattered light when pulsed light is incident on an optical fiber by spirally winding the outer circumference of the shielding layer or the insulating layer at a pitch of 2.5 to 20 times the outer diameter of the shielding layer or the insulating layer. To detect the local temperature rise asymmetric with respect to the cable center axis in a short section of the cable by measuring the time change of the intensity ratio of light to anti-Stokes light, and to detect the ground fault of the power cable early. It is possible to calculate the distance from the cable terminal to the accident occurrence point, and it is possible to locate the accident occurrence point.

[Brief description of drawings]

FIG. 1 is a partially exploded view of an optical fiber composite power cable according to a first embodiment of the present invention.

FIG. 2 is a sectional view of an optical fiber composite power cable according to a first embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of an optical fiber core wire.

FIG. 4 is a sectional view of an optical fiber composite power cable according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a distributed temperature measurement system.

FIG. 6 is an explanatory diagram of a Raman scattering principle.

FIG. 7 is a diagram showing temperature dependence of Raman scattered light intensity.

FIG. 8 is an example of measurement of Raman scattered light intensity.

FIG. 9 is an example of temperature measurement by measuring Raman scattered light intensity.

FIG. 10 is a diagram showing an outline of a cable ground fault pseudo-fault test method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber composite power cable (first embodiment) 1A Optical fiber composite power cable (second embodiment) 2 Cable center conductor 3 Inner semiconductive layer 4 Crosslinked polyethylene insulation layer 5 External semiconductive layer 7 Optical fiber core wire 7a Optical fiber element wire 7b Powder lubricant 7c Metal layer 8 Shielding layer 9 Cable sheath (sheath) 20 Measuring unit 21 Optical unit 22 Pulse light source 23 Spectroscopic device 24 Photoelectric conversion unit 25, 26 Light receiving element 27, 28 Amp (amplifier) 29 Digital Averaging Unit 30 Computer

Claims (2)

[Claims] 1. A power cable in which a cable center conductor is insulated with an insulator, a shield layer including an outer conductor is provided on an outer periphery of the insulator, and a jacket is provided on an outer periphery of the shield layer. An optical fiber core wire is provided on a part of the optical fiber core wire along the longitudinal direction thereof, and the optical fiber core wire is 2.5 to 2 times the outer diameter of the shielding layer.
An optical fiber composite power cable characterized by being wound around the outer periphery of the insulator at a pitch of 0 times and capable of detecting an accident of the power cable based on the Raman scattered light intensity of the optical fiber core wire. 2. A power cable in which a cable center conductor is insulated with an insulator, and an outer jacket is provided on the outer circumference of the insulator, wherein an optical fiber core wire is provided in a part of the outer jacket along the longitudinal direction thereof. , The optical fiber core wire with the outer diameter of the insulator 2.
An optical fiber composite power cable characterized in that it can be wound around the outer periphery of the insulator at a pitch of 5 to 20 times and an accident of the power cable can be detected based on the Raman scattered light intensity of the optical fiber core wire.